n the Arizona of 1874, Marshal Sam Mackenna (Gregory Peck) of Hadleyburg learns the location of the hidden canyon, known as the Valley of Gold, that the legend says is where the Apaches stashed sacred gold. The marshal is ambushed in the desert and forced to shoot Prairie Dog, an old Apache chief. Before dying, the Indian for some reason entrusts Mackenna with a map of the mythical canyon but warns him that the Apache gods watch over their gold. The marshal memorizes and then burns the map. He is then captured by a ruthless gang of Mexican bandits, led by Colorado (Omar Sharif).